Did this once.
The Environment was small so the Helpdesk did this as manual task.
No idea if this is the correct way but it worked for us.
Find the users SID in the new Domain, you will need it later
import-module ActiveDirectory
get-aduser testuser
Logoff the user
Rename the profile Folder as Administrator - replace old SID with new SID
Mount the VHDX as Administrator
Edit \Profile\Appdata\Local\fslogix\ProfileData.reg
Delete the line with "Sid" and the line with "Guid"
Replace the SID in the first line with the new SID.
Unmount the VHDX
Logon user with new Domain.
Thomas